Exhaust system of an internal-combustion engine

ABSTRACT

The exhaust gases of a two-bank internal-combustion engine are guided, by way of exhaust gas collectors, to a central expansion chamber of a housing. From there, they flow through main catalysts arranged on opposite ends of the housing, before they are guided into the open air by way of end mufflers. 
     This exhaust system provides a space-saving arrangement of all components required for an optimal emission control, and low exhaust gas back pressure, and meets all acoustic requirements.

BACKGROUND AND SUMMARY OF THE INVENTION

The invention relates to an exhaust system of a multi-cylinderinternal-combustion engine, the exhaust gases of which are guided bymeans of a collector approximately centrically to a housing which hascatalysts at opposite ends, all exhaust gas being lead out to the openair downstream of the catalysts.

In the German Patent Document DE- 2 452 675, an exhaust system isdisclosed in which the exhaust gases flow by way of a collector into aninterior housing surrounded by an exterior housing. In this case, theexhaust gases first reach an afterburning chamber in a central mannerand are guided from there as separate flows through two catalystsarranged on opposite ends of the interior housing into the exteriorhousing, in which the exhaust gas flows are mixed again and reach theopen air by way of a common exhaust.

From the German Patent Document DE- 21 17 771, an exhaust system isknown in which pipe sections, which extend from one cylinder bankrespectively of the internal-combustion engine into a muffler, have aperforated construction inside this muffler. The German Patent DocumentDE-39 30 380 shows an exhaust system of a multi-cylinderinternal-combustion engine in which starting catalysts are connectedinto the exhaust pipes which are connected directly to the cylinderhead, which starting catalysts have a central duct, which can be closedby a flap, and a ring duct which surrounds it and contains the catalystmaterial.

The invention is based on the object of providing an exhaust system foran internal-combustion engine which, while its arrangement isspace-saving, has a low exhaust back pressure and achieves an optimalexhaust emission control.

This object is achieved by means of an arrangement of the above-notedtype wherein the collector is provided with an end piece which projectsinto an expansion chamber which is centrally arranged in the housing.

The low exhaust back pressure is achieved by the central arrangement ofthe expansion chamber and the complete symmetrical acting upon thecatalysts which follows.

The discharge of the exhaust gases flowing through the catalysts by wayof separate exhausts also provides a symmetrical low exhaust backpressure. Furthermore, the central position of the expansion chamberpermits a space-saving arrangement of this chamber and of the adjacentcatalysts in a common housing. The exhaust gases can be guided to thecatalytic emission control system by way of short pipes and lines. Thus,the catalysts rapidly reach their temperature required for an optimalemission control.

The flowing of the exhaust gases into the expansion chamber arrangedcentrally in the housing and the dividing into two separate exhaust gasflows that takes place there, which exhaust gas flows act directly,without any reduction of the cross-section, upon the main catalysts byway of large-surface perforated metal sheets, permits a fast parallelflowing through the main catalyst monoliths and the subsequentdischarging of the purified exhaust gases by way of one separate exhaustrespectively.

The low exhaust back pressure promotes a good power development of theinternal-combustion engine while the fuel consumption is reduced at thesame time. The arrangement of the housing transversely with respect tothe longitudinal direction of the internal-combustion engine permits asymmetrical arrangement of the lines and offers a large space for thehousing of the main catalysts. A large catalyst volume is theprerequisite for a long working life of the catalyst.

A damper volume surrounding the catalysts acts in a damping mannertogether with the expansion chamber arranged in front of the maincatalysts which, on the one hand, results in acoustic advantages and, onthe other hand, reduces pressure peaks in the exhaust gas flow whichotherwise may result in damage to the catalysts or to the whole housing.The large volume of the exhaust system has a damping effect on pressurefluctuations.

According to the working volume of the internal-combustion engine andaccording to acoustic requirements, all exhaust pipes together may beguided in an exhaust collector into the expansion chamber or a separatecollector may be assigned to one cylinder bank respectively.

For acoustic and fluidic reasons as well as because of the componentstrength, it was found to be advantageous to close the end pieces of thecollector in the expansion chamber at the end and to let the exhaustgases flow out by way of openings on their lateral surface.

In order to meet also the strictest emission control regulations,starting catalysts may be inserted in the exhaust collector orcollectors whose small monolith mass, because of the arrangement closeto the combustion chamber, reaches its working temperature particularlyfast.

These starting catalysts may have, for example, as switchable catalysts,ring-shaped monoliths which surround an at first closed central duct.After the working temperature of the main catalysts has been reached,the central duct is opened up so that the exhaust gas will no longerflow through the monoliths. For a particularly fast-acting emissioncontrol, a separate starting catalyst, which is inserted in therespective exhaust pipe, may be assigned to each individual cylinder ofthe internal-combustion engine.

In an advantageous development of the invention, the housing may beconstructed in a double-walled manner as a heat exchanger and may beprovided with connection pieces. By way of these connection pieces, thefresh air to be heated is supplied which is heated by the energycontained in the exhaust gases and is then, by way of additionalconnection pieces, supplied, for example, to the interior of a vehicleequipped with such an exhaust system.

For the control of the fuel-air mixture of the internal-combustionengine and for the monitoring of the operatability of the catalysts,several lambda probes are arranged in the exhaust system. The control ofthe mixture, in this case, is carried out by, in each case, one or twofirst lambda probes arranged upstream of the catalysts, while second orthird probes arranged downstream of catalysts are used for the catalystmonitoring.

Other objects, advantages and novel features of the present inventionwill become apparent from the following detailed description of theinvention when considered in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view from below of a first embodiment of theinvention;

FIG. 2 is a schematic view from below of a second embodiment of theinvention;

FIG. 3 is a schematic view from below of a third embodiment of theinvention; and

FIG. 4 is a sectional view along Line IV--IV according to FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS

An internal-combustion engine installed in a motor vehicle has twocylinder banks 1, 2 in an opposed arrangement. On the cylinder heads 3,4, exhaust pipes 6 are arranged which start out from individualcylinders 5 and are brought together in one connection piece 7 for eachcylinder bank 1, 2. Exhaust collectors 8 are connected to theseconnection pieces 7 and feed the exhaust gas of the cylinder banks 1, 2to a housing 9. This housing 9 extends on the end face of theinternal-combustion engine transversely to its longitudinal direction Fand has an oval-surface cross-section (FIG. 4). The two lines 8 with theend pieces 11, which are closed with a cover 12 at the end and haveradial openings 14 on their lateral surface 13, lead perpendicularlyinto a centrally disposed expansion chamber 10.

On both sides of the chamber 10, a circular pipe section 15 is arrangedwhich bounds the chamber 10 by means of a face-side perforated metalsheet 16 and is held, at its end, in a closing lid 17 of the housing 9.Inside the section 15, two monoliths 19 are axially spaced which form amain catalyst 18. Thus, a damping volume V is formed between the housing9, a closing lid 17, a metal sheet 16 and a pipe section 15respectively.

On both sides outside the housing 9, an exhaust 20 for the exhaust gasesis arranged which comprises an end muffler 21 connected with the closinglid 17 as well as an end pipe 22 connected with the open air.

According to a first embodiment of the invention (FIG. 1), switchablestarting catalysts 25 are arranged in the collectors 8, which startingcatalysts 25 have a central duct 27 which can be closed by means of aflap 26 and have a ring duct 28 containing the catalyst material. Thecollectors 8 may be guided together before they enter into the expansionchamber 10 so that only an end piece 11 is arranged centrically in thischamber 10 (FIG. 3).

For the monitoring of the operatability of the main and startingcatalysts 18, 25 as well as for the control of the fuel-air mixture fedto the internal-combustion engine, several lambda probes are arranged inthe exhaust system which detect the oxygen content in the exhaust gas.Two first probes L1 are arranged upstream of the starting catalysts 25;a second probe L2 is arranged in the expansion chamber 10 and two thirdprobes L3 are arranged downstream of the main catalysts 18.

In a second embodiment according to FIG. 2, the expansion chamber 10 isdivided by means of a wall 29 into two partial chambers 30, 31, one endpiece 11 respectively leading into the partial chamber 30, 31. In thiscase, one lambda probe L2 is arranged in each partial chamber 30, 31.

According to this embodiment, the housing 9 is constructed in adouble-walled manner as a heat exchanger 32. By way of an inlet, whichis not shown, fresh air to be heated is fed to the heat exchanger 32.This fresh air is heated by means of the thermal energy contained in theexhaust gases and, by way of connection pieces 33, is guided as heatingair into the interior of the motor vehicle.

In both embodiments of the invention, instead of a starting catalyst 25in a collector 8, a separate starting catalyst 25 may be assigned toeach exhaust pipe 6 of a cylinder 5.

The third embodiment according to FIG. 3 shows an exhaust system withoutstarting catalysts 25, in which the exhaust collectors 8 are broughttogether before entering into the expansion chamber 10 and lead intothis chamber 10 by means of a joint end piece 11; however, two endpieces 11 according to FIG. 1 may also be provided. A first lambda probeL1 is arranged in the chamber 10 and a second probe L2 is in each casearranged downstream of the main catalysts 18.

The heat exchanger 32 may be optionally provided in the case of allmentioned embodiments.

The respective first lambda probes L1 are used for controlling thefuel-air mixture; the second and third probes L2 and L3 are used for themonitoring of the catalysts 18, 25.

Since a control is always desired that is as fast as possible, in thethird embodiment (FIG. 3), one first probe L1 respectively may bearranged in each connection piece 7. By means of the differential signalbetween the first and second or second and third probes L1, L2 or L2,L3, the operatability of the catalysts 18, 25 is monitored.

During the operation of the internal-combustion engine, the exhaustgases are guided in the exhaust system along the entered arrows.Immediately after the start of the internal-combustion engine, when thecentral duct 27 is closed, the exhaust gas is guided via the ring ducts28 where it rapidly heats up the comparatively small starting catalysts25 and therefore causes an early exhaust gas purification.

In a manner not described in detail, the flaps 26 open up the centralduct 27 when the light-off temperature of the main catalysts 8 isreached, so that the exhaust gases, following the path of the lowestresistance, no longer flow through the ring duct 28 or flow through thering duct 28 only to a slight extent, whereby the service life isincreased.

Subsequently, the collectors 8 lead the exhaust gas by way of the endpieces 11 to the expansion chamber 10. According to the first and thirdembodiment, the exhaust gases of all cylinders 5 of theinternal-combustion engine are mixed at the latest in the chamber 10,are then divided into two identical exhaust gas flows A which flowthrough the main catalysts, and are then lead into the open air throughone exhaust 20 respectively.

According to the second embodiment of the invention, no mixing takesplace of the exhaust gas of the cylinder banks 1, 2 as a result of thewall 29. In this case, the exhaust gas is guided and treated completelyseparately for each cylinder bank 1, 2.

In all embodiments, the damping volume V is coupled to the volume of theexpansion chamber 10 by way of breakthroughs 34 (FIG. 4) in the metalsheets 16.

Although the invention has been described and illustrated in detail, itis to be clearly understood that the same is by way of illustration andexample, and is not to be taken by way of limitation. The spirit andscope of the present invention are to be limited only by the terms ofthe appended claims.

I claim:
 1. An exhaust system of a multi-cylinder internal-combustionengine, the exhaust gases of which are guided by means of a collectorapproximately centrally to a housing which has catalysts at oppositeends, all exhaust gas being led out to the open air downstream of thecatalysts, wherein the collector is provided with an end piece whichprojects into an expansion chamber which is centrally arranged in thehousing, said end piece being provided with radial openings on itslateral surface.
 2. A system according to claim 1, comprising cylinderscombined in two banks and exhaust pipes leading from the cylinders tothe collector, wherein a collector is assigned to each cylinder bank andleads by means of an end piece into the expansion cylinder, each saidend piece being provided with radial openings on its lateral surface. 3.A system according to claim 1, wherein the housing extends transverselywith respect to the longitudinal direction (F) of theinternal-combustion engine.
 4. A system according to claim 1, whereinthe expansion chamber is cylindrically constructed, and wherein the endpieces lead perpendicularly into the cylindrically constructed expansionchamber.
 5. A system according to claim 2, wherein the end pieces areclosed at the end.
 6. A system according to claim 2, wherein eachexhaust gas collector has a catalyst.
 7. A system according to claim 6,wherein each starting catalyst has a closable central duct and a ringduct which surrounds it and contains the catalyst material.
 8. A systemaccording to claim 1, wherein the housing is constructed in adouble-walled manner as a heat exchanger provided with connection pieceswhich heats fresh air means of the thermal energy of the exhaust gases.9. A system according to claim 2, wherein a wall bounding partialchambers is arranged in the expansion chamber between the end pieces.10. A system according to claim 1, wherein lambda probes are arrangedupstream of at least one catalyst.
 11. A system according to claim 2,wherein the catalysts include at least one starting catalyst and atleast one main catalyst, and wherein lambda probes are arranged upstreamof each starting catalyst and downstream of each main catalyst and inthe expansion chamber.
 12. A system according to claim 2, wherein aseparate starting catalyst is assigned to each exhaust pipe.
 13. Asystem according to claim 4, wherein each exhaust gas collector has acatalyst.
 14. A system according to claim 5, wherein each exhaust gascollector has a catalyst.
 15. A system according to claim 4, whereinlambda probes are arranged upstream of at least one catalyst.
 16. Asystem according to claim 6, wherein lambda probes are arranged upstreamof at least one catalyst.
 17. A system according to claim 4, wherein thecatalysts include at least one starting catalyst and at least one maincatalyst, and wherein lambda probes are arranged upstream of eachstarting catalyst and downstream of each main catalyst and in theexpansion chamber.
 18. A system according to claim 4, wherein thecatalysts include starting catalysts, and wherein a separate startingcatalyst is assigned to each exhaust pipe.
 19. A system according toclaim 1, wherein lambda probes are arranged downstream of at least onecatalyst.
 20. A system according to claim 4, wherein lambda probes arearranged downstream of at least one catalyst.
 21. A system according toclaim 6, wherein lambda probes are arranged downstream of at least onecatalyst.
 22. An exhaust system of a multi-cylinder internal-combustionengine, the exhaust gases of which are guided by means of a collectorapproximately centrally to a housing which has catalysts at oppositeends, all exhaust gas being led out to the open air downstream of thecatalysts, wherein the collector is provided with an end piece whichprojects into an expansion chamber which is centrally arranged in thehousing, and wherein lambda probes are arranged upstream of at least onecatalyst.
 23. An exhaust system of a multi-cylinder internal-combustionengine, the exhaust gases of which are guided by means of a collectorapproximately centrally to a housing which has catalysts at oppositeends, all exhaust gas being led out to the open air downstream of thecatalysts, wherein the collector is provided with an end piece whichprojects into an expansion chamber which is centrally arranged in thehousing, and wherein lambda probes are arranged upstream of at least onecatalyst.